1. Field of the Invention
The present invention relates to an optical pickup apparatus, more particularly to an optical pickup apparatus for recording/reproducing information on/from an optical disc on a compact disc player, a laser vision disc player, or like.
2. Description of the Prior Art
In general, an optical pickup apparatus records and reproduces information on and from an optical disc by converging optical beams on the optical disc.
When the optical pickup apparatus records information on an optical disc, an optical beam radiated from a semiconductor laser is focused on an information recording surface of the optical disc as a shape of beam spots and elevates the temperature of the information recording surface up to the Curie point. Then, the information recording surface loses the coercive force and is magnetized so as to correspond to the given external magnetic field. Thereafter, the radiation of the optical beam is stopped and the external magnetic field is maintained as it is, and the temperature of the information recording surface is lowered. When the temperature comes down under the Curie point, the magnetized information recording surface is maintained as it is even though the external magnetic field is changed so that the recording of the information is completed.
When the optical pickup apparatus reproduces information from an optical disc, the semiconductor laser radiates an optical beam at a temperature below the Curie point onto the information recording surface of the optical disc. Then, the information recording surface has a Kerr effect, or magneto-optical effect, on the focused optical beam, so that the polarizing plane of the optical beam is rotated at an angle depending upon the magnetized state of the information recording surface. The optical pickup apparatus reproduces the information on the optical disc by detecting the magnetized state of the information recording surface based on the rotated angle of the polarizing plane.
An optical disc has an information track formed thereon in concentric or spiral shape at an interval of about 1.6 micrometer. The optical pickup apparatus records/reproduces data on/from a predetermined position of an optical disc by means of the information track. Therefore, the optical pickup apparatus performs focusing servo and tracking servo in order to exactly record and reproduce data on and from the optical disc. That is, the optical pickup apparatus controls the optical beam to be focused on the information track and to precisely follow it. Accordingly, the optical pickup apparatus detects servo error signals including focusing error signal and tracking error signal, and an objective lens actuator adjusts an objective lens along the focusing and tracking direction based on the detected servo error signals.
FIG. 1 is a schematic constructional view of a conventional optical pickup 10 for an optical disc player as described above.
As shown in FIG. 1, an optical pickup apparatus 10 of an optical disc player which is used in general includes a first semiconductor substrate 4 having a predetermined shape and size. A second semiconductor substrate 4a is arranged on a upper portion of first semiconductor substrate 4, and on the center of the upper surface of the second semiconductor substrate 4a a semiconductor laser 1 radiating laser beams is mounted.
Also, a polygonal prism 2 is arranged at a predetermined interval apart from semiconductor laser 1 on another upper portion of first semiconductor substrate 4. Photodetectors 3 and 3a are disposed on a boundary surface between the bottom of prism 2 and the upper surface of first semiconductor substrate 4, which change the intensity of a laser beam modulated and reflected by the optical disc.
Further, an objective lens 5 is disposed apart from an incline surface 7 of prism 2 at a predetermined interval.
In the optical pickup apparatus according to prior art which has the above construction, the semiconductor laser I emits a laser beam having a vibration wavelength of 780 nm.+-.20 nm. The laser beam emitted from semiconductor laser 1 is reflected at a predetermined angle by incline surface 7 of prism 2, is transmitted through objective lens 5 toward optical disc 6, and then is focused on about 1 .mu.m area of optical disc 6.
The laser beam focused on the information recording surface of optical disc 6 is reflected by optical disc 6 and returns through objective lens 5 toward prism 2 after its intensity is modulated depending on the size of a pit 6a having information recorded thereon. As the laser beam reflected by optical disc 6 is refracted by incline surface 7 of prism 2 and is transmitted toward first photodetector 3, a part of the laser beam is received by first photodetector 3 and the rest of the laser beam is reflected toward the upper surface of prism 2. The laser beam reflected to the upper surface of prism 2 is reflected toward a second photodetector 3a again, and as a result is received by second photodetector 3a. First and second photodetectors 3 and 3a convert the optical information into an electrical signal depending on the intensity of the laser beam which has been received. Also, first and second photodetectors 3 and 3a detect focusing and tracking errors, and then transmits them to the servo system (not shown) so as to perform focusing and tracking controls.
Since optical pickup apparatus 10 of the optical disc player according to prior art as described above includes two photodetectors 3 and 3a, two photodetectors increase the cost of the optical disc player. Also, it is the disadvantage that the laser beam reflected by optical disc 6 is reflected several times by prism 2 in order to divide the laser beam into two laser beams. Accordingly, the loss of the laser beam increases and the optic efficiency decreases.
To solve the above described problems, various efforts for providing an optical pickup apparatus comprising a prism which can be easily manufactured and which can effectively utilize the intensity of the laser beam have been tried.
U.S. Pat. No. 5,164,930 issued to Satoshi Sugiura discloses an optical pickup apparatus comprising a prism which can be easily manufactured and which can effectively utilize the intensity of laser beam. The optical pickup apparatus of Satoshi Sugiura includes a semiconductor substrate, a light-emitting device, a beam splitting device, and a light diffracting device, and can effectively utilize the intensity of the laser beam by reducing the transmission path of the beam emitted from semiconductor laser. In the optical pickup apparatus of Satoshi Sugiura, however, it is difficult to assemble two photodetectors and a light wave guiding member for guiding the diffracted beam toward the second photodetector which are disposed in the semiconductor substrate.